An “atomic layer‐by‐layer” structure of Co3O4/graphene is developed as an anode material for lithium‐ion batteries. Due to the atomic thickness of both the Co3O4 nanosheets and graphene, the composite exhibits an ultrahigh specific capacity of 1134.4 mAh g−1 and an ultralong life up to 2000 cycles at 2.25 C, far beyond the performances of previously reported Co3O4/C composites.

Sodium-ion batteries (SIBs) have been attracting intensive attention at present as the most promising alternative to lithium-ion batteries in large-scale electric storage applications, due to the low-cost and natural abundance of sodium. Elemental phosphorus (P) is very promising anode material for SIBs, with the highest theoretical capacity of 2596 mAh g −1 . Recently, there have been many efforts devoted to phosphorus anode materials for SIBs. As pure red phosphorus can not react with Na reversibly, many attempts to prepare composite materials containing phosphorus have been reported. Here, we report the facile preparation of a red phosphorus/N-doped carbon nanofiber composite (P/NCF) that can deliver a reversible capacity of 731 mAh g -1 in sodium-ion batteries (SIBs), with capacity retention of 57.3 % over 55 cycles. Our results suggest that it would be a promising anode candidate for SIBs with a high capacity and low cost.

Exploring economically efficient electrocatalysts with good electrocatalytic activity is essential for diverse electrochemical energy devices. Series of ultrathin metallic nickel-based holey nitride nanosheets were designed as bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). They exhibit improved catalytic properties owing to the inherent advantages of their plentiful active reaction sites resulting from the complete exposure of the atoms in the large lateral surfaces and from the edges of pore areas, together with expanded lattice spacing distance. This obtained three-dimensional conductive integral architecture can not only accelerate the electron transportation by the highly orientated crystalline structure but also facilitate the diffusion of intermediate and gases. In terms of the OER electrocatalytic properties, a quite low overpotential (300 mV) is required for the holey two-dimensional (2D) Ni3Fe nitride nanosheets to deliver a current density of about 100 A g-1, with an enhanced improvement over IrO2by a factor of nearly 25 times. The holey 2D Ni3Fe nitride nanosheets also exhibit enhanced catalytic performance toward the HER, with a tiny overpotential (233 mV) to achieve a current density of about 100 A g-1with much better kinetic properties in comparison to those of highly active Pt/C.

Carbon-encapsulated Sn@N-doped carbon tubes with submicron diameters were obtained via the simple reduction of C@SnO@N-doped carbon composites that were fabricated by a hydrothermal approach. Sn nanoparticles encapsulated in carbon layers were distributed uniformly on the surfaces of the N-doped carbon nanotubes. The electrochemical performances of the composites were systematically investigated as anode materials in sodium-ion batteries (SIBs). The composite electrode could attain a good reversible capacity of 398.4 mAh g when discharging at 100 mA g, with capacity retention of 67.3% and very high Coulombic efficiency of 99.7% over 150 cycles. This good cycling performance, when compared to only 17.5 mAh g delivered by bare Sn particles prepared via the same method without the presence of N-doped carbon, could be mainly ascribed to the uniform distribution of the precursor SnO on the substrate of N-doped carbon tubes with three-dimensional structure, which provides more reaction sites to reduce the diffusion distance of Na, further facilitating Na-ion diffusion and relieves the huge volume expansion during charging/discharging. These outcomes imply that such a Sn/C composite would provide more options as an anode candidate for SIBs.

Hierarchical SnO2 hollow spheres self-assembled from nanosheets were prepared with and without carbon coating. The combination of nanosized architecture, hollow structure, and a conductive carbon layer endows the SnO2 -based anode with improved specific capacity and cycling stability, making it more promising for use in lithium ion batteries.

In this work, amorphous carbon very thin layers coated on a Nb 2 O 5 nanosheet flexible composite have been successfully synthesized. The composite delivers a discharge capacity of 396 mA h g À1 after 100cycles at a current density of 100 mA g À1 , which is very much higher than for bare Nb 2 O 5 nanosheets.

Capacitive storage (e.g., double layer capacitance and pseudocapacitance) with Na + stored mainly at the surface or interface of the active materials rather than inserted into the bulk crystal is an effective approach to achieve high rate capability and long cycle life in sodium-ion batteries (SIBs). Herein, atomically thin Co 3 O 4 nanosheets are successfully synthesized and grown directly on the stainless steel mesh as an anode material for SIBs. This anode delivers a high average capacity of 509.2 mAh g −1 for the initial 20 cycles (excluding the first cycle) at 50 mA g −1 , presents excellent rate capability with an average capacity of 427.0 mAh g −1 at 500 mA g −1 , and exhibits high cycling stability, which significantly outperforms the electrode prepared from conventional Co 3 O 4 nanostructures, the electrode prepared by conventional casting method, and previously reported Co 3 O 4 electrodes. The superior electrochemical performance is mainly attributable to the atomic thickness of the Co 3 O 4 nanosheets and the direct growth method in electrode processing, which lead to remarkably enhanced surface redox pseudocapacitance and interfacial double layer capacitance. This Na + capacitive storage mechanism provides a promising strategy for the development of electrode materials with high energy and power densities and ultralong cycle life for SIBs.

Germanium (Ge) is a prospective anode material for lithium-ion batteries, as it possesses large theoretical capacity, outstanding lithium-ion diffusivity, and excellent electrical conductivity. Ge suffers from drastic capacity decay and poor rate performance, however, owing to its low electrical conductivity and huge volume expansion during cycling processes. Herein, a novel strategy has been developed to synthesize a Ge@N-doped carbon nanotubes (Ge@N-CNTs) composite with Ge nanoparticles uniformly distributed in the N-CNTs by using capillary action. This unique structure could effectively buffer large volume expansion. When evaluated as an anode material, the Ge@N-CNTs demonstrate enhanced cycling stability and excellent rate capabilities.